Irrometer Tensiometers

[Savage Henry]

I've said it before: I suck at judging wet/dry cycles. Yes, I know and use the picking up the pots technique. It doesn't have the precision I'm a fan of and is problematic once everything is in a trellis. I've also been determining et rates roughly by subtracting the amount of runoff from the total irrigation volume daily. Alas, I continually find myself overwatering. my yields have been fine (.65-.75 gpw on average) but properly-judged irrigation cycles are one of the missing pieces in my puzzle, and will probably help with the recurring fungus gnats as well.

So, naturally, I did a bit of research. The irrometer brand Tensiometers came up several times, used by a couple quite reputable growers (clackamas coot and spurr, specifically). Since I'm growing in 1-2gal pots of coir I ordered a couple mlt models (http://www.irrometer.com/pdf/IRROMETERs/111 Model MLT Web 6.pdf)

I'm stoked to have a quantitative value to log, and will be able to determine an optimal amount of irrigation cycles based on this (along with continual qualitative analysis, of course).

So spurr suggests irrigating when the moisture level of the coir gets to 5-7kpa according to the meter. I'll see what the plants look like/how the pots feel at this level.

Does anyone else use these devices? If so how do you like em? I read in an older thread that @Fresh Starts was considering it.

Thanks, as always.


Edit: here's a pretty great read about soilless irrigation, with a section on tensiometer-based irrigation:http://lieth.ucdavis.edu/pub/Pub073_RavivLieth_SoillessCulture_Ch04.pdf

 

[Savage Henry]

Oh, wow. Check this study out: http://journal.ashspublications.org/content/126/5/638.full.pdf

They optimized irrigation with Tensiometers for roses, looks like spurr was spot on with his kpa set points:

 

[Natural]

I've got a friend that says he's putting them into beds..I don't think he has yet. They def come in different depth sizes and I think they only last so long. They look tons better than some unreliable blumats that's for sure

 

[noone88]

I've been advocating dry cycles for a while. "let the medium get dry". I would further add to it that it is very important to let the medium dry out at least a handful of times during veg and early flower. However, once you're in flower and up until the last week or so, you should not let the medium dry out due to salt toxicity. It's kinda simple really, once the amount of water drops very low, your salt concentration skyrockets to very high levels. Plus, the plant during weeks 3-7 of flower is growing at a rapid pace and you should feed it right up to the point of nutrient burn.

Anyways, you'll see more and more precision watering as the industry progresses. Stuff like floracaps makes the watering very precise. I know for our table rooms, we feed specific amounts to each rockwool cube via emitters. Soil/soilless is harder due to the unknown mass of the root system. however, i've been hand watering since 2009. You just develop a feel for things.

 

[Savage Henry]

I've got a friend that says he's putting them into beds..I don't think he has yet. They def come in different depth sizes and I think they only last so long. They look tons better than some unreliable blumats that's for sure

That's pretty cool, I could see them being super handy in beds. Coot was talking about getting a couple of them at different lengths to use outdoors in those huge 300gal pots. Then one could watch the moisture drain from the top and water em when the lower portion begins to dry out.

Apparently the porous ceramic tips are the first thing to go on em, luckily there's replacement parts available, so I ordered a couple. Thanks for reminding me.

I've been advocating dry cycles for a while. "let the medium get dry". I would further add to it that it is very important to let the medium dry out at least a handful of times during veg and early flower. However, once you're in flower and up until the last week or so, you should not let the medium dry out due to salt toxicity. It's kinda simple really, once the amount of water drops very low, your salt concentration skyrockets to very high levels. Plus, the plant during weeks 3-7 of flower is growing at a rapid pace and you should feed it right up to the point of nutrient burn.

Anyways, you'll see more and more precision watering as the industry progresses. Stuff like floracaps makes the watering very precise. I know for our table rooms, we feed specific amounts to each rockwool cube via emitters. Soil/soilless is harder due to the unknown mass of the root system. however, i've been hand watering since 2009. You just develop a feel for things.

Totally, boss. Never any need to let them dry out to the point of the salts crystallizing and the medium ex skyrocketing. I've totally fried roots this way in the past. When I'm referring to wet/dry cycles at this point I mean field capacity/~50% capacity.:)

I've been reading quite a bit about how guys are running rockwool and I agree, precision is key. I like using pc drip emitters for this purpose, as I can gauge pretty damn close how much they're getting watered. I'm about to flip a run in root bound 1 gal pots, in pretty excited to see how many irrigation cycles they demand, I'm thinking 6-12/day by the end of stretch.

 

[Halosmoker]

Here's some good reading on them. I use them in my Notill beds. http://lieth.ucdavis.edu/Research/tens/98/SmtPub.htm

 

[Savage Henry]

Have you picked up/used a tensiometer yet? I've been interested in this very subject for awhile. I grow in 20g pots and beds and find it extremely difficult to know the best time to water which for me is every 24-48h. I know how important it is to get it just right cuz there are always a few plants that are MUCH nicer than the average and those ones dry out fastest. I've put data loggers n meters around them and come to realize it isn't anything special about their particular location temp/rh/circulation wise that's giving them the edge it's the optimal wet/dry cycles those particular plants are experiencing. I'm now switching to all beds/troughs in an effort to level the playing field in terms of moisture plus I've seen the amazing results unrestricted lateral root growth provides. I've tried various moisture meters w limited success since a high medium ec will schew readings plus I'll lift /dig/probe my pots top and bottom in an effort to determine wetness but it all seems inadequate to me- I wanna know w certainly. I've seen some pricey moisture meters that you can manually calibrate that sound good but they will likely still b affected by ec. What are your thoughts ? :D

They should be here this week, so I can't speak to experiences with them. That said, the irrometer site says that they're not affected by soil salinity, so we'll see how it goes. I'll post some updates on here as I get the hang of em.

 

[Savage Henry]

Here's some good reading on them. I use them in my Notill beds. http://lieth.ucdavis.edu/Research/tens/98/SmtPub.htm

An extremely helpful reference. Thank you, sir.

 

[Halosmoker]

Glad to be of help

 

[Savage Henry]

In anticipation of the arrival of my new toys I weighed one of the pots I used (empty), filled it with coir, weighed it again, then drenched it with water, waited a half hour for it to drain, then weighed it again. I subtracted the weight of the pot and the dry coir to determine its water holding capacity. The only issue is figuring the true volume of the pots, as a typical one gallon nursery pot is rarely 1 gallon by volume, ime. I suppose I can empty out the pot into a container with measurements on it to determine the air holding capacity of the medium when it's fully saturated.

 

[Savage Henry]

@Wentworth thanks, but it wasn't my own idea, pieced it together from some white papers I've been reading.

I beleive LT is the one for your situation. The other ones appear to be for soils with more of a clay content in orchards and for row crops. Try technodepot.com, that's where I got mine, and I *think* they ship worldwide.

Interesting history of the pot sizes, I think us canna growers may be the only ones referring to them as 1gal, it looks like the ag industry at large calls em #1 size.

As far as the length of the meter it looks like you want it long enough so the tip sits like halfway down into your pot. If you haven't already, read the link @Halosmoker posted, it answered a bunch of my questions.

Have you seen the irrometer lysimeters? They just might be my next purchase, no more sme or pour-thru methods for testing medium ec...

 

[Savage Henry]

My drip system is fairly primitive, just a submersible pump into 3/4 line into drippers, I control this with a timer. The jawns that control a solenoid look awesome but I went analog for now, perhaps I'll upgrade later. Cool thing is it looks like one can switch out the different gauges on it, so I wouldn't have to buy an entire new unit.

I did watch a video on what you're talking about, though, there's a whole section of them on the irrometer website. The one you may want to look at is here:

Edit:
You want to order the service unit with them as well, looks like it's needed to configure the thing.

 

[Smokey503ski]

The tension meter i seen a few days ago uses negative air pressure to wick the solution.
I'll get a link.

 

[Savage Henry]

The mailman was good to me today:

@Smokey503ski sounds pretty cool, I'd be interested in seeing that.

 

[Halosmoker]

Awesome

 

[Savage Henry]

I ordered the spare tips on top of the Tensiometers, they were like $15usd each, so worth it for the piece of mind. but the Tensiometers have a 1 year warranty, have to remember to send in the registration card.

Let my know how the lysimeters work for you when you get em, those things look so cool...

The books are pretty antiquated, I'm a cheap ass so the version of the Howie Resh book I got is from 1995, there are pictures of computer-controlled irrigation systems and the computer takes up an entire room, lol. The newest version apparently has an entire chapter on coir, whereas this one doesn't mention it at all, I'll probably buy it eventually. But this version does have a section on determining crop nutrition thru tissue analysis, which is something I want to get into, so it should still be of some help.

 

[Smokey503ski]

The mailman was good to me today:View attachment 636749

@Smokey503ski sounds pretty cool, I'd be interested in seeing that.

Looks like the same thing my boy at QiCompany uses.
I honestly thought it was a penis pump when he pulled it out of the box.

 

[Smokey503ski]

@Savage Henry did yours come with a drill bit so you can easily insert to your medium?

 

[Savage Henry]

Looks like the same thing my boy at QiCompany uses.
I honestly thought it was a penis pump when he pulled it out of the box.

Lol, yea the pump for the larger tensiometers certainly resembles one.

@Savage Henry did yours come with a drill bit so you can easily insert to your medium?

No drill bit, so I'm going to have to get creative. I have a soil core sampler that should work. Spurr mentioned that they work best when installed during transplant but none of the information from the manufacturer speaks to this.

 

[Smokey503ski]

Lol, yea the pump for the larger tensiometers certainly resembles one.



No drill bit, so I'm going to have to get creative. I have a soil core sampler that should work. Spurr mentioned that they work best when installed during transplant but none of the information from the manufacturer speaks to this.

I'll find some info out on it. Makes sense why you would use one.